1. Field of the Invention
The present invention relates, to an ion exchange apparatus with an enhanced reliability of regeneration operation and a simplified construction of a salt water supply device.
2. Description of the Related Art
Ion exchange apparatuses for removing hardness components (e.g., calcium ion and magnesium ion), nitrate nitrogen (e.g., nitrate ion and nitrite ion), and so on in raw water such as tap water and underground water, by adsorbing them on an ion exchange resin bed have been known in the art. Among those ion exchange apparatuses, one that substitutes sodium ion or potassium ion for hardness components in water for by using a cation exchange resin is referred to as a water softener. In contrast, among those ion exchange apparatuses, one that substitutes chloride ion for nitrate nitrogen by using an anion exchange resin is referred to as a nitrate nitrogen remover.
When the total amounts of adsorbed specific ions (hardness components and nitrate nitrogen), which are to be removed, reach a predetermined limit of exchange capacity, the ion exchange resin bed begins to leak the specific ions into treated water. Therefore, before the total amounts of the adsorbed specific ions exceed the predetermined limit of exchange capacity, the ion exchange apparatus performs a regeneration operation of bringing the ion exchange resin bed into contact with salt water (specifically, an aqueous sodium chloride solution) to recover its exchange capacity.
The general construction of the ion exchange apparatus is disclosed in, for example, JP 04-108586 A. The ion exchange resin bed is housed in a bomb-shaped resin cylinder (resin tank) having an opened upper part. The top of the resin cylinder is provided with a flow passage control valve for switching between water service operation and regeneration operation. In addition, the ion exchange apparatus is provided with a salt water tank reserving salt water and a salt water valve arranged in the salt water tank, which serve as a salt water supply device for supplying salt water to the ion exchange resin. The salt water valve is connected to the flow passage control valve through the salt water supply line. The salt water tank is designed such that the user supplies regeneration salt regularly to thereinto to generate the salt water.
The regeneration operation generally includes a backwash process, a regeneration process, an extrusion process, a rinsing process, and a water-refill process, which are performed in the stated order. So, the salt water valve is configured to actuate in accordance with the respective processes. In the regeneration process, raw water is passed through an ejector installed in the flow passage control valve and salt water in the salt water tank is then supplied to the ion exchange resin bed using a negative pressure generated in the ejector. At this time, the salt water valve operates to open a passage from the inside of the salt water tank to the flow passage control valve and then operates to block air suction due to the action of a float ball when the salt water is consumed to a predetermined water level. Subsequently, the process switches to the extrusion process when the salt water valve is closed. In other words, in the ion exchange apparatus, the shift from the regeneration process to the extrusion process depends on the operation of the salt valve, and with regard to the processing times for the regeneration process and the extrusion process, only the total processing time is defined.
Further, in the water-refill process, refill water is supplied from the flow passage control valve to the salt water tank. At this time, the salt valve operates to open a passage from the flow passage control valve to an inside of the salt water tank, while it operates to block an injection of refill water by the action of a float valve when the supply of refill water reaches to a predetermined water level. The salt water valve can be produced in mass production from molded parts using a corrosion-resistant synthetic resin material, so it has been employed as a standard mechanism in the ion exchange apparatus.
By the way, in the ion exchange apparatus, the amount of refill water to be supplied is controlled by the operation of the salt water valve. Therefore, when the float valve is stuck by crystalline salt, refill water is not sufficiently supplied, and thus the desired amount of salt water cannot be produced. In addition, in the ion exchange apparatus, the amount of salt water to be supplied is controlled by the operation of the salt water valve. Thus, for example, when the user has forgotten to refill regeneration salt, the desired amount of salt water cannot be produced. Further, in the ion exchange apparatus, the shift from the regeneration process to the extrusion process depends on the operation of the salt water valve. Thus, for example, when the pressure of raw water against the ejector is lowered or when the line for supplying the salt water is clogged, the amount of salt water to be supplied and the amount thereof to be extruded become insufficient. Those deficiencies result in insufficient regeneration and extrusion of the ion exchange resin bed, so such deficiencies have often been constituted causes in deterioration of treated water to be supplied.
Further, the salt water valve has a large number of parts, so the salt water supply device has a complicated construction. Thus, the use of the salt water valve requires much time in assembling and maintenance, thereby causing an increase in costs for production and maintenance.